In the fertiliser industry, granules of a fertiliser salt or other fertiliser, preferably having a particle size of 1-4 mm, are required in increasing quantities because of the use of mechanical spreaders. These granules are mainly produced in the potash industry by the use of the so-called press granulation method. In this method, the fine-grained fertiliser salt is first pressed in a roll press to give a so-called shell which is formed into granules in a subsequent disintegration-sieve stage. The strength of the granules depends to a very high degree on the pre-treatment of the potassium salt. Salts which are produced by a crystallisation process and which have not been mixed with a so-called anti-caking medium can, in general, be formed as granules of high strength. In contrast, granules produced from flotation salts are less strong. This results from the fact that chemical residues from the flotation process, in particular amines, adhere to the surface of the primary granules and interfere with the formation of a strong binding. Such types of granules are, in many cases, subjected to an after-treatment process which consists essentially of the step damping followed by drying. It is an object of this after-treatment to keep abrasion during handling (for example during bunkering, loading and transport) low and to limit the dust nuisance which is connected with it. For this purpose dust-binding media are sometimes added to the liquid used for damping.
If the surface of the granules or other bulk material is damped with an amount of water between 0.5 and 2% of the weight of the material there is produced during the subsequent drying of the material a strengthening of the periphery of the apparatus thereof, as a result of which the resistance of the granules to abrasion is increased.